TY - JOUR
T1 - Comparative GC-EAD Responses of A Specialist (Microplitis croceipes) and A Generalist (Cotesia marginiventris) Parasitoid to Cotton Volatiles Induced by Two Caterpillar Species
AU - Ngumbi, Esther
AU - Chen, Li
AU - Fadamiro, Henry Yemisi
N1 - Funding Information:
EAD responses to headspace volatiles collected from cotton damaged by its host species (H. virescens) than to headspace volatiles collected from cotton that was damaged by the non-host species (S. exigua). Our GC data showed that the essential difference between the volatile blends induced by H. virescens vs. S. exigua is in the amounts and consequently the ratios of the same compounds. De Moraes et al. (1998) also reported that the main difference in the volatile blends of plants damaged by H. virescens vs. H. zea was in the ratios of identical compounds. Those authors further reported that the specialist parasitoid C. nigriceps could distinguish behaviorally plants damaged by its host, H. virescens from those damaged by H. zea (a non-host species), possibly by exploring the differences in the ratios of identical compounds in the volatile blends. Thus, the differences recorded in our study in the ratios of the same compounds in the blends induced by the two caterpillar species may be exploited by M. croceipes to differentiate plants damaged by its host from non-host species. This proposition is supported by our GC-EAD results which showed greater response of M. croceipes to volatiles from H. virescens damaged plants, compared to S. exigua damaged ones. The need to discriminate hosts from related non-hosts based on subtle differences in the ratios of identical compounds in blends is without doubt a challenging task for specialist parasitoids, such as M. croceipes. Thus, it is likely that other unknown minor compounds as well as host-specific volatiles also may play a role in differentiation of host vs. non-host by M. croceipes.
PY - 2009/10
Y1 - 2009/10
N2 - Plants emit volatile blends that may be quantitatively and/or qualitatively different in response to attack by different herbivores. These differences may convey herbivore-specific information to parasitoids, and are predicted to play a role in mediating host specificity in specialist parasitoids. Here, we tested the above prediction by using as models two parasitoids (Hymenoptera: Braconidae) of cotton caterpillars with different degree of host specificity: Microplitis croceipes, a specialist parasitoid of Heliothis spp., and Cotesia marginiventris, a generalist parasitoid of caterpillars of several genera including Heliothis spp. and Spodoptera spp. We compared GC-EAD (coupled gas chromatography electroantennogram detection) responses of both parasitoid species to headspace volatiles of cotton plants damaged by H. virescens (a host species for both parasitoids) vs. S. exigua (a host species for C. marginiventris). Based on a recent study in which we reported differences in the EAG responses of both parasitoids to different types of host related volatiles, we hypothesized that M. croceipes (specialist) would show relatively greater GC-EAD responses to the herbivore-induced plant volatile (HIPV) components of cotton headspace, whereas C. marginiventris (generalist) would show greater response to the green leaf volatile (GLV) components. Thirty volatile components were emitted by cotton plants in response to feeding by either of the two caterpillars, however, 18 components were significantly elevated in the headspace of H. virescens damaged plants. Sixteen consistently elicited GC-EAD responses in both parasitoids. As predicted, C. marginiventris showed significantly greater GC-EAD responses than M. croceipes to most GLV components, whereas several HIPV components elicited comparatively greater responses in M. croceipes. These results suggest that differences in the ratios of identical volatile compounds between similar volatile blends may be used by specialist parasitoids to discriminate between host-plant and non-host-plant complexes.
AB - Plants emit volatile blends that may be quantitatively and/or qualitatively different in response to attack by different herbivores. These differences may convey herbivore-specific information to parasitoids, and are predicted to play a role in mediating host specificity in specialist parasitoids. Here, we tested the above prediction by using as models two parasitoids (Hymenoptera: Braconidae) of cotton caterpillars with different degree of host specificity: Microplitis croceipes, a specialist parasitoid of Heliothis spp., and Cotesia marginiventris, a generalist parasitoid of caterpillars of several genera including Heliothis spp. and Spodoptera spp. We compared GC-EAD (coupled gas chromatography electroantennogram detection) responses of both parasitoid species to headspace volatiles of cotton plants damaged by H. virescens (a host species for both parasitoids) vs. S. exigua (a host species for C. marginiventris). Based on a recent study in which we reported differences in the EAG responses of both parasitoids to different types of host related volatiles, we hypothesized that M. croceipes (specialist) would show relatively greater GC-EAD responses to the herbivore-induced plant volatile (HIPV) components of cotton headspace, whereas C. marginiventris (generalist) would show greater response to the green leaf volatile (GLV) components. Thirty volatile components were emitted by cotton plants in response to feeding by either of the two caterpillars, however, 18 components were significantly elevated in the headspace of H. virescens damaged plants. Sixteen consistently elicited GC-EAD responses in both parasitoids. As predicted, C. marginiventris showed significantly greater GC-EAD responses than M. croceipes to most GLV components, whereas several HIPV components elicited comparatively greater responses in M. croceipes. These results suggest that differences in the ratios of identical volatile compounds between similar volatile blends may be used by specialist parasitoids to discriminate between host-plant and non-host-plant complexes.
KW - Cotesia marginiventris
KW - GC-EAD
KW - Green leaf volatiles
KW - Heliothis virescens
KW - Herbivore-induced plant volatiles
KW - Microplitis croceipes
KW - Spodoptera exigua
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UR - http://www.scopus.com/inward/citedby.url?scp=70350392803&partnerID=8YFLogxK
U2 - 10.1007/s10886-009-9700-y
DO - 10.1007/s10886-009-9700-y
M3 - Article
C2 - 19802643
AN - SCOPUS:70350392803
SN - 0098-0331
VL - 35
SP - 1009
EP - 1020
JO - Journal of Chemical Ecology
JF - Journal of Chemical Ecology
IS - 9
ER -